Multilayer laminates, containers and other articles have numerous applications in industry, particularly for packaging applications. Kirk-Othmer Encyclopedia of Chemical Technology, Third edition, Volume 10, page 216 (1980), Wiley-lnterscience Publication, John Wiley & Sons, New York, details generally the materials and processes required for making such articles as well as their applications. Another article of interest, for example, is "Films, Multilayer," by W. Schrenk and E. Veazey, Encyclopedia of Polymer Science and Engineering, Vol. 7, 106 (1980). Generally, such articles are prepared by coprocessing individual polymers in injection or extrusion operations or by laminating individually formed layers together or by a combination of these processes. Coprocessing as discussed herein refers to forming and/or subsequently processing at least two layers of polymeric material, each layer comprising a different polymeric material. Common polymers used in these applications include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-methyl acrylate copolymer, polyvinyl chloride, polyvinylidene chloride, polyamide, polyester, polycarbonate, polystyrene, acrylonitrile copolymers and the like. Desired properties in the laminates, films, sheets and the like, depend on the intended applications but generally include good mechanical properties such as tensile and impact strengths, processability, tear resistance, gas barrier properties, moisture barrier properties, optical properties, thermal and dimensional stability and the like.
U.S. Pat. No. 5,256,351 to Lustig et al and U.S. Pat. No. 5,283,128 to Wilhoit disclose biaxially stretched thermoplastic films from polyethylene and a process to prepare them. U.S. Pat. No. 5,460,861 to Vicik et al also teaches improved multilayer films from polyolefins. U.S. Pat. No. 4,911,963 to Lustig et at discloses an oriented multilayer film from nylon. U.S. Pat. No. 5,004,647 to Shah describes a coextruded multilayer film comprising ethylene-vinyl alcohol copolymer.
Many methods of forming useful articles from combinations of polymers require that all components of the combination be stretched, expanded or extended in one or more directions, or deformed in some other way, such as by folding, creasing and the like. This stretching, extending or other deformation may be carried out concurrently with the process of forming the laminate or individual layers from the melt or may be part of a subsequent forming operation. Deformation can also be a requirement of using the article. Such methods of forming include but are not limited to, uniaxial and biaxially stretching of extruded films, thermoforming of multilayer laminates, blowing of extruded or injection-molded tubes, stretch blow molding of preforms or parisons, creasing or folding of laminates to form boxes, twisting of films to form a wrapper and the like.
Combining layers of different polymers is a method generally used to form a multilayer laminate which takes advantage of the different properties which may be available in the different polymer layers while also minimizing the amount of the more expensive polymer used.
Many methods of container formation require the collapse of a tube or the folding of a multi-layer structure. In such cases, it is desirable to avoid wrinkles, to ensure that the various layers remain bonded to each other and to avoid fracturing or tearing one of the layers. Other methods of container formation require uniform stretching or expansion of the multilayer laminate at temperatures sufficient to stretch any polymeric material present in the laminate. It is advantageous to be able to coprocess the laminate, for example, to fold, stretch, expand or compress it without fracturing, tearing or otherwise destroying the integrity of any layer.
Thermotropic liquid crystal polymers are polymers which are liquid crystalline (i.e., anisotropic) in the melt phase. Other terms, such as "liquid crystal", "liquid crystalline" and "anisotropic" have been used to describe such polymers. These polymers are thought to possess a parallel ordering of their molecular chains. The state in which the molecules are so ordered is often referred to as either the liquid crystal state or the nematic phase of the liquid crystalline material. These polymers are prepared from monomers which are generally long, flat and fairly rigid along the long axis of the molecule.
Generally, liquid crystal polymers ("LCPs") have properties that are very desirable, such as excellent chemical resistance, high mechanical strength, and excellent gas, moisture and aroma barrier properties. It can be, however, difficult to heat-bond articles made of LCPs together or to other materials. It also may be difficult to write or print on articles made from LCPs.
LCPs are more expensive than conventional polyesters. Additionally several conventional LCPs even in the form of thin films do not possess high optical clarity. In general LCPs cannot be stretched or deformed more than a few percent unless they are heated to a processing temperature range of from about 200.degree. C. to about 320.degree. C., preferably from about 220.degree. C. to about 300.degree. C. Generally film and bottle formation processes require an excess of 100% elongation. For amorphous LCPs having no measurable melting point, this processing temperature range is referred to as the "molten state". In addition, in this temperature range where conventional LCPs can be deformed, they have very low melt strength and are weak. Tubes from conventional LCPs cannot be collapsed without wrinkling. Films or laminates containing one or more conventional LCP layers are difficult to fold without delamination and splitting. Preforms or parisons containing conventional LCP layers will have fractures or tears in the LCP layer unless they are heated to or are in the molten state before stretching, which may be far too high a temperature for coprocessing the other layers in the laminate.
U.S. Pat. No. 4,384,016 to Ide et at discloses that when polymers which exhibit anisotropic properties in the melt phase (i.e., thermotropic liquid crystal polymers) are extruded through a slit die and drawn in the melt phase, films and sheets which exhibit high machine direction properties are obtained. However, Ide et at recognizes that such films or sheets possess poor transverse directional properties which may limit their usefulness in certain structural applications and proposes laminating uniaxially oriented sheets at angles to one another to provide a multiaxially oriented sheet.
Stretching or drawing of the laminated, multiaxially oriented sheet proposed by Ide et al is not disclosed.
Another method for producing a multiaxially oriented liquid crystal polymer film is proposed by Harvey et at in U.S. Pat. No. 5,288,529 wherein axially flowing liquid crystal polymer material is subjected to transverse directional forces to strain the axial flow, and then the microscale structural orientation obtained is solidified to achieve a liquid crystal polymer film with nearly isotropic mechanical properties. Harvey et at proposes a process of shear orientation during extrusion to overcome the deficiencies in the mechanical properties of liquid crystal polymer films, which films are disclosed as being inadequate for certain applications because they can not be blown and drawn after extrusion as coil polymers (such as polyethylene terephthalate) can. More specifically, it is disclosed that liquid crystal polymer films which comprise relatively straight, or fibrillar, molecules become highly oriented in the die in the direction of extrusion and the flowing liquid crystal polymer becomes anisotropic, more so than ordinary coil polymers which tend to randomize. Because the liquid crystal polymer becomes highly oriented in the die anisotropically, it is disclosed that it may not be possible to stretch the polymer substantially in the direction transverse to its fibrillar orientation.
U.S. Pat. No. 5,534,209 to Moriya discloses that many of the physical properties of liquid crystal polymers are very sensitive to the direction of orientation of the liquid crystal regions in the polymer. This may be very desirable for linear products such as filaments and fibers, but anisotropic properties are often undesirable in products having a planar forms, such as tape, films, sheets and the like. Moriya also discloses that shear orientation processes such as those disclosed in Harvey et al have a drawback in that they are unable to make thin multiaxially oriented films without the formation of pinholes, tears and other imperfections. Moriya states that in the case of melt-processed thermotropic liquid crystal polymers which have very high processing viscosity, it is difficult to obtain films with uniform surface smoothness and thickness by shear orientation processes. This further increases the film's tear sensitivity as well as its susceptibility to curling and streaking.
Moriya obtains a liquid crystal polymer film having random orientation by feeding a thermotropic liquid crystal polymer into a melt region formed in the nip between opposed inward facing surfaces of two support membranes. The randomly oriented liquid crystal polymer film formed by the Moriya process may be multiaxially oriented by stretching the sandwich structure formed by the liquid crystal film and the two support membranes at or above the melting point of the liquid crystal polymer.
U.S. Pat. Nos. 5,364,669 and 5,405,565 to Sumida et al both disclose composite films comprising a layer of liquid crystal polymer having gas barrier properties, an adhesive layer, and a thermoplastic layer formed from thermoplastics such as polyalkylene terephthalates, olefin polymers, nylons, polycarbonates and the like. The composite films are suitable as a food packaging material. Sumida et al discloses that molten liquid crystal polymer may be biaxially stretched from the melt but should be extruded downward from the die to prevent the problems associated with low melt viscosity and weakness of the melted film which create difficulties when the molten liquid crystal polymer film is extruded upward from the die. Examples of the Sumida et al process are provided wherein Vectra.RTM. A900 (a trademark of Hoechst Celanese Corporation of Somerville, N.J.) wholly aromatic liquid crystal polyester resin is extruded at 290.degree. C. at a blow ratio of 5.5 and a draft ratio of 6.0 to obtain a multiaxially oriented liquid crystal polymer film. Blow molding and stretch blow molding to obtain bottles or jars are not disclosed.
It is often desirable to obtain shaped articles from multilayer laminates by thermoforming and/or blow molding processes because they are cost effective methods of making mass produced shaped articles. However, such processes often are either not practical or not possible with materials that must be melt stretched, such as the wholly aromatic Vectra.RTM. liquid crystalline resins and other melt-processable liquid crystalline polymers utilized in the processes described above. Thus, it would be desirable to have a stretchable liquid crystalline polymer which may be stretched not only when in the molten state, but also at temperatures above the T.sub.g of the liquid crystalline polymer but below the molten state, or stretchable below about 200.degree. C. Furthermore, it would also be desirable to have laminates and articles formed from such laminates comprising a layer of such a stretchable liquid crystalline polymer layer.
Often, copolymers or blends of different constituent polymeric materials are used to provide a combination of properties in the resulting copolymer or blend that none of the individual constituent polymeric materials possess by themselves. For example, it might be proposed to combine a melt-processable liquid crystalline material having excellent mechanical and gas barrier properties together with a thermoplastic polymeric material in an attempt to obtain a blend or copolymer having gas barrier properties, good mechanical properties and stretchability at lower temperatures.
However, it has been recognized that such combinations, prepared either as copolymers or blends, may exhibit what is termed a "negative synergistic effect". That is, even if the polymers are compatible in combination and form a copolymer or blend, the combination of polymers may have less desirable properties than would have been predicted. The exact mechanism for this effect is not fully understood, but often the properties in the copolymer or blend are closer to a combination of the least desirable properties of each individual constituent polymer, rather than the best properties of each. Even when good properties are obtained, the resultant polymeric material may have certain shortcomings.
U.S. Pat. No. 5,326,848 to Kashimura et al discloses thermotropic liquid crystal polyesters produced by a hybrid copolymerization process wherein polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or copolymers of PET and PEN are combined with conventional liquid crystal polyester structural units based on hydroxy naphthoic acid and hydroxy benzoic acid, or units based on hydroxy naphthoic acid alone. Kashimura et al proposes to achieve both excellent formability and gas barrier properties and discloses laminates having layers of the liquid crystal polyester compositions with layers of other polymers such as polyesters, polyolefins and polyamides to produce laminated containers such as cups and bottles. A polyester composition capable of preparing formed shapes by deep drawing an unstretched sheet is disclosed as comprising PET combined with units based on hydroxy naphthoic acid and hydroxy benzoic acid. However, it is disclosed that the gas barrier property of this deep drawing composition may sometimes be inferior to the gas barrier properties obtained by the other compositions disclosed which are not disclosed as suitable for deep drawing. In all of the liquid crystal polyester compositions disclosed by Kashimura et al, an aliphatic dihydroxy component must be present in at least 15 mol percent in the liquid crystalline polyester. Although the formation of bottles and blow molding are disclosed, neither are demonstrated, nor are draw ratios for bottle formation or blow molding disclosed. Biaxial stretching of a film of the composition heated to 100.degree. C. to 240.degree. C. at a ratio of 3.times.3 is disclosed.
The processes disclosed by Kashimura et al for producing liquid crystalline polyester compositions consist of reacting a polymer such as PET, PEN or copolymers of these polyesters together with monomers based on hydroxy naphthoic acid and hydroxy benzoic acid or hydroxy naphthoic acid alone. This hybrid polymer/monomer copolymerization is necessitated by the requirement that at least 15 mol percent of the liquid crystalline polyester composition be an aliphatic dihydroxy component. This aliphatic component must be combined with the terephthalic acid and/or naphthalene dicarboxylic acid component before it is combined with the liquid crystal polyester monomeric moieties because it prevents the formation of the desired hybrid polymer. The process disclosed by Kashimura et al for producing such LCPs is highly variable and, therefore, difficult to develop into a full-scale commercial process to obtain liquid crystal polymer compositions in substantial quantities.
Stretchable multilayer laminates and articles comprising an LCP layer have been proposed. For example, JP 5,177,797 A discloses that multilayer containers may be prepared from a laminate comprising layers of a thermoplastic resin and an LCP. Other disclosures of similar nature and of interest include, for example, JP 5,177,796 A; JP 1,199,841 A; JP 5,169,605 A; and WO 9,627,492 A.
Pending application, Ser. No. 08/761,042, filed Dec. 5, 1996, discloses laminates comprising an LCP layer in the middle and peelable thermoplastic layers on the outside. Pending patent application, Ser. No. 081761,109, filed Dec. 5,1996, discloses polarizer laminates comprising dyed LCP layer in the middle and non-peelable thermoplastic layers on the outside. Pending applications, Ser. Nos. 08/954,377, 08/954,378, and 08/954,997 disclose adhesives for making multilayers at least one of those layers being from an LCP.
It would be desirable to produce stretchable LCPs and also to produce multilayer laminates or articles having one or more LCP layers bonded to one or more non-LCP layers to obtain a multilayer structure having the best properties of all of the various layers, such as a multilayer structure having good gas barrier properties, mechanical properties, optical properties and relatively low cost. It would be desirable for such liquid crystalline polymers and multilayer structures to be stretchable not only at temperatures where the LCP composition is in the molten state, but also at lower temperatures, above the T.sub.g of the LCP composition, but below the temperature range where the LCP composition is in the molten state. It would be desirable to be able to stretch such an LCP or LCP laminate more than once and achieve high draw ratios. It would be desirable to produce an LCP for such a laminate via a predictable, stable process, capable of use on a large commercial scale.